According to Einstein's theory of special relativity, it is impossible for an object with mass to reach or exceed the speed of light in a vacuum. There are several key reasons why this is the case:
Mass-Energy Equivalence: Special relativity establishes the famous equation E = mc², which shows that mass and energy are interchangeable. As an object accelerates, its kinetic energy increases. As it approaches the speed of light, the energy required to continue accelerating it also increases. At the speed of light, an infinite amount of energy would be needed to accelerate an object with mass, which is not feasible.
Time Dilation: Special relativity states that as an object accelerates and approaches the speed of light, time dilation occurs. Time slows down for the moving object relative to a stationary observer. As the object's speed increases, time dilation becomes more pronounced, making it increasingly difficult to reach the speed of light. At the speed of light, time would essentially stop for the object.
Length Contraction: According to special relativity, as an object's speed increases, its length in the direction of motion contracts. This phenomenon is known as length contraction. As the object approaches the speed of light, its length in the direction of motion shrinks, making it physically impossible to reach or exceed the speed of light.
These fundamental principles of special relativity place a theoretical limit on the speed at which objects can travel in the universe. While particles without rest mass, such as photons, can travel at the speed of light, objects with mass would require an infinite amount of energy and experience infinite time dilation and length contraction to reach or exceed the speed of light, which is not achievable in practice.